Tektronix TCP300 Series, User Manual, Page: 46 / 80

Reference Notes
Measuring Noncontinuous Current with the TCP404XL Probe
When you measure a noncontinuous current with the TCP404XL probe, you
need to take into consideration several factors to ensure that you make accurate
measurements and do not trip the thermal overload circuit. The amplitude
and duty cycle of the continuous and noncontinuous current, and the ambient
temperature, all affect the maximum amount of time allowed for the measurement,
which de
fi nes the safe operating area of the probe.
You can calculate the duty cycle of the continuous and noncontinuous
current when you know the duration of the noncontinuous current (de
fi ned as
measurement time) and the measurement period. A continuous and noncontinuous
current is shown and how to calculate the duty cycle. (See Figure 14.)
Figure 14: Duty cycle calculation
After you calculate the duty cycle of the noncontinuous current you are measuring,
you can use the other factors (continuous and noncontinuous current amplitude,
etc.) to compare your measurement to those shown. (See Figure 34 on page 56.)
(See Figure 36 on page 57.)
You can see how duty cycle affects the measurement time by looking at any of
the three graphs. (See Figure 34 on page 56.) (See Figure 36 on page 57.) As the
duty cycle increases on the x-axis, the measurement time (of the noncontinuous
current) on the y-axis decreases.
The effect of measuring two different noncontinuous current amplitudes, 750 A
and 600 A respectively, with varying duty cycles and levels of continuous current
is illustrated. (See Figure 34 on page 56.) (See Figure 35 on page 56.) The
ambient temperature in these two examples is kept constant at 50 °C.
28 TCPA300/400 Ampli fi ers and TCP300/400 Series Current Probes User Manual